Allow wquque to use callback to free an mbuf - so

mbufs can be reused/pooled

src/wqueue.c

@@ -24,7 +24,7 @@ static int uc_wqueue_handle_write(struct UCWQueue *wqueue)
 
         mbuf = uc_mbuf_dequeue(&wqueue->queue);
         assert(mbuf != NULL);
-        uc_mbuf_free(mbuf);
+        wqueue->free_cb(mbuf);
         wqueue->queue_len--;
     }
 
@@ -71,7 +71,7 @@ void uc_wqueue_init(struct UCWQueue *wqueue, struct IOMux *mux)
     memset(wqueue, 0, sizeof *wqueue);
     wqueue->mux = mux;
     wqueue->fd.callback = uc_wqueue_cb;
-    
+    wqueue->free_cb = uc_mbuf_free;
     uc_tailq_init(&wqueue->queue);
 }
 
@@ -81,7 +81,7 @@ int uc_wqueue_clear(struct UCWQueue *wqueue)
     int rc = 0;
 
     while ((buf = uc_mbuf_dequeue(&wqueue->queue)) != NULL) {
-        uc_mbuf_free(buf);
+        wqueue->free_cb(buf);
         wqueue->queue_len--;
     }